Jordan Katzman and Alex Fenkell are now two of the youngest billionaires in the US.

Shares of the direct-to-consumer dental-product company they cofounded, SmileDirectClub, began trading on Nasdaq on Thursday. SmileDirectClub closed down 28% after its first day of trading, but its market cap of $6.4 billion made Katzman and Fenkell — each of whom owns close to a quarter of the company's class B shares — billionaires.

SmileDirectClub sells invisible teeth aligners for $1,850, a fraction of the cost of traditional braces from an orthodontist, Business Insider reported.

A SmileDirectClub representative did not immediately return Business Insider's request for comment on Katzman and Fenkell's personal relationship, current involvement in the business, and personal fortunes.

Katzman and Fenkell grew up to become serial entrepreneurs.

A garage for luxury cars in Shenzhen, China. Katzman and Fenkell started a car-detailing business before founding SmileDirectClub.
Reuters/Thomas Peter

Before SmileDirectClub, Katzman and Fenkell launched a car-detailing business and software that allowed people to build a single shopping list of items pulled from multiple websites, according to Inc.

"It took Jordan and I years to find the right idea and you have to be willing to fail a few times beforehand to succeed," Fenkell told the Michigan Fashion Media Summit, an event that SmileDirectClub sponsored. "It's important to not get hung up on just one idea, you need to be willing to move forward and pivot when something isn't working."

Katzman and Fenkell founded SmileDirectClub just five years ago, in 2014.

Employees at a SmileDirectClub store.
AP Photo/Jae C. Hong

The pair secured funding from Camelot Venture Group, an investment firm run by Katzman's father, David Katzman, according to Forbes.

Their goal was to revolutionize the teeth-straightening industry as Crest Whitestrips revolutionized the teeth-whitening industry by letting people whiten their teeth at home, Fenkell told Inc.

They originally named the business SmileCareClub, according to Inc.

David Katzman told the cofounders to build a website for the new business to see if there was any interest from potential customers, according to the Nashville Business Journal. So many people visited the site that it crashed within days.

David Katzman became the new company's CEO.

David Katzman at the company's initial public offering on Thursday.
REUTERS/Lucas Jackson

Katzman, 59, is also SmileDirectClub's largest shareholder. Forbes reported on September 3 that he was expected to have an estimated net worth of about $2 billion after the company's initial public offering.

Katzman had experience with direct-to-consumer businesses, having invested in 1-800-Contacts and Quicken Loans through Camelot, according to SmileDirectClub's website. Katzman held positions at Home Depot, the Cleveland Cavaliers, and Fathead, a wall-decal company, before SmileDirectClub, according to the Nashville Business Journal.

Jordan Katzman's uncle, Steven Katzman, is SmileDirectClub's chief operating officer. Between Jordan, David, and Steven, the Katzman family will control more than 65% of the voting power, CNBC reported.

Fenkell has repeatedly defended SmileDirectClub during the company's squabbles with competitors.

SmileDirectClub has also faced substantial opposition from dentists and orthodontists who say that straightening your teeth without an in-person consultation with a medical professional can do more harm than good, the Detroit Free Press reported last year.

SmileDirectClub said in a press release in 2017 that it was "a target of a well-funded lobbying and public relations effort by the American Association of Orthodontics (AAO), the largest orthodontist industry group, which is seeking to shut down pioneers of innovative, affordable teledentistry services."

"If industry lobbyists have their way, millions of Americans will be denied access to a healthy smile through teledentistry," Fenkell said in the release. "It's important that we stand up for those who, without SmileDirectClub, would not have access to an affordable new smile."

He told Inc. last year: "Whenever you disrupt something, there's going to be some friction. It just takes some time to muscle through the first year of the business, to show the results, and we believe we've done that."

SmileDirectClub has even filed lawsuits against its detractors, including the Georgia and Alabama dental boards, according to the Nashville Business Journal.

Fenkell said he didn't spend time worrying about worst-case scenarios.

A dental assistant looking at a scanned image of a patient's teeth in SmileDirectClub's SmileShop inside a CVS store in California.
Associated Press

If SmileDirectClub loses its lawsuits against the state dental boards, the company could be forced to overhaul its business model to include closer oversight of patients by dentists, the Nashville Business Journal reported last year.

"We would have to assess if that became the case," Fenkell told the publication. "We just believe so strongly in what we're doing ... I just can't see that."

Other young American billionaires include the Stripe cofounders Patrick and John Collison, 31 and 29, the Snapchat founder Evan Spiegel, 29, and the social-media mogul Kylie Jenner, 22, according to Forbes.

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